McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 4 1 Drugs affecting the male reproductive system

The evidence

BOX 41.3

tadalafil ( Cialis ) and vardenafil ( Levitra ). Box 41.3 contains more information about Viagra. Therapeutic actions and indications When injected directly into the cavernosum, alprosta- dil acts locally to relax the vascular smooth muscle and allow filling of the corpus cavernosum, causing penile erection. The PDE5 inhibitors sildenafil, tadalafil and vardenafil are selective inhibitors of cyclic guanosine monophosphate (cGMP). The PDE5 inhibitors are taken orally and act to increase nitrous oxide levels in the corpus cavernosum. Nitrous oxide activates the enzyme cGMP, which causes smooth muscle relaxation, allowing the flow of blood into the corpus cavernosum. They prevent the breakdown of cGMP by phosphodiesterase, leading to increased cGMP levels and prolonged smooth muscle relaxation, thus promoting the flow of blood into the corpus cavernosum, resulting in penile erection. The prostaglandin alprostadil and the PDE5 inhib- itors are indicated for the treatment of penile erectile dysfunction. The PDE5 inhibitors have the advantage of being oral drugs that can be timed in coordination with sexual activity, based on the drug’s onset. Silde- nafil ( Revatio ) is also approved for the treatment of pulmonary arterial hypertension. By relaxing smooth muscle, the pulmonary artery relaxes and there is less Viagra—wonder drug? The release of the drug Sildenafil (Viagra) to treat penile erectile dysfunction caused a tremendous stir in society. This was the first oral drug developed to treat a disorder that was common in ageing men but was seldom mentioned or discussed. Viagra, which facilitates penile erection approximately 1 hour after it is taken, returned sexual function to many of these men. For many months after its release, the drug was the centre of controversy, news coverage and debate. Stand-up comedians, television situation comedies and Internet joke networks were buzzing with the latest Viagra jokes. Insurance companies debated covering the cost of this drug. Was it like cosmetic surgery, and not a necessary treatment, or was it a necessary aid to human physiology? Most insurance companies ended up covering the cost of Viagra. Women’s rights groups voiced concern that no drug was approved and covered to help facilitate a woman’s sexual response. Viagra is in trial stages for the treatment of sexual dysfunction in women; early reports seem to indicate that it is not effective. However, Viagra has proven to be very effective at increasing sexual functioning for many men. Its success has led to the development of two new drugs in the same class of phosphodiesterase type 5 (PDE5) inhibitors, tadalafil (Cialis) and vardenafil (Levitra). The use of these drugs is not without risks. Deaths have occurred when these drugs were combined with

resistance and pressure in the pulmonary bed. Tadalafil is also approved for daily use in men who are very active sexually. A person might select this drug if the timing of sexual stimulation is not known and may be several hours away. See Table 41.3 for usual indications for all four of these drugs. Pharmacokinetics After injection, alprostadil is metabolised to inactive compounds in the lungs and excreted in the urine. The PDE5 inhibitors are well absorbed from the GI tract, undergo metabolism in the liver and are excreted in the faeces. The differences among the three PDE5 inhibitors lie in their onset and duration of action. Sildenafil has a median onset of 27 minutes and duration of 4 hours. People are encouraged to take the drug 1 hour before anticipated sexual stimulation. Vardenafil has a mean onset of action of 26 minutes and duration of 4 hours; it is also intended to be taken 1 hour before sexual stimu­ lation. Tadalafil has an onset of action of 45 minutes and duration of 36 hours. None of these drugs is indicated for use in women, so no adequate studies have been done during pregnancy and breastfeeding. Because the effects on pregnancy are not known, if alprostadil is being used, condoms should be used during intercourse with a pregnant woman. providers are often asked for specific prescription drugs based on media advertising.This relatively new phenomenon in healthcare presents new challenges to the healthcare provider to ensure quality teaching to help the person understand the actual uses, effects and rationales for a specific drug therapy. nitrates (e.g. glyceryl trinitrate) or alpha-adrenergic blockers. Headache, flushing, stomach upset and urinary tract infections often occur.There have been reports of sudden loss of vision and hearing.These drugs can be used only once daily, and they do not work without sexual stimulation. Absorption is delayed if they are taken with a high-fat meal, and people need to plan accordingly. People also should be reminded that they need to use protection against sexually transmitted infections. When Viagra was the hot, new drug, there was tremendous demand for it from the public.This demand put healthcare providers in the position of ensuring that the drug was right for the person’s actual needs.The cause of penile erectile dysfunction should be determined, if at all possible. If this is a problem that the person has never before discussed with the healthcare provider, there could be an underlying medical condition that should be addressed.The adverse effects, timing of administration and drug combinations to avoid should be discussed with the person before the drug is prescribed. With pharmaceutical companies now advertising in magazines, on television and over the Internet, healthcare